Parents may have to buy new textbooks rather than second-hand ones when some secondary school subjects are merged under education reforms, the Consumer Council said.

Under the voluntary pilot scheme, starting in September, schools can choose between teaching traditional subjects separately or adopting broader integrated subjects such as culture and heritage, personal and social development, resources and environment, and social systems and citizenship.

Publishing companies have started preparing new editions ahead of the change, which is part of the education reforms and may become mandatory in a few years. "If we want to be in the business, we have to follow in the line of the educational reforms," MacMillan Publishers (China) marketing director Tommy Cheung Wai-to said.

The changes, affecting Forms One to Three, mean parents could not buy used books or pass books from one sibling to the next. Textbooks in Form One, Two and Three cost in total an average of $2,127, $1,904 and $1,885 respectively last year, according to the Consumer Council.

The Education Department said it did not have an estimate of how many schools would join the voluntary scheme.